Why I usually have ulcers in mouth after eating sour things? Why I usually have ulcers in mouth after eating sour things? It is complicated. Sour things are acidic. Acid causes dehydration. When dehydration goes beyond normal limits body supplies lot of fluids to the area which is acidic. There is fine control in this area. Our blood acid should never go beyond the normal range of 7.35 to 7.45....